nice guide, but just want to mention that you haven't found a way to kill the tarrasque. It will eat some of itself, thereby not starving, and regenerating as normal (which doesn't cause hunger, it's not like growing, you don't ever need to eat to renerate).

Other than that quite inspiring, but I wouldn't want to play one anyway, too fight focused, not enough fun and too powerful. But this is no critique on your guide.

honestly I would let him do it, really it's okay to stick by the rules.

Of course if he ever stops cackling because someone goes out of range or he doesn't have a move action left he can't cast fortune on that person again for 24hours (not just until he sleeps 8h).
So before any real fight just give a few challenges to see if he still wants that move action. Don't always do it, but sometimes just let him climb, avoid falling rocks, let him swim or fly somewhere or whatever.

Also just for the fun of it, let them meet a boss who got 100 witches in his well defended castle cellar who have fortune, scar (for the distance) and cackle and really have nothing else to do than let him reroll every round 100 dice. Human lvl 1 spellcaster services should be affordable. (and yes I'm pretty sure that multiple cackles from different witches stack)
And if they are high enough levels and you're really pissed make it a vorpal weapon and reroll till you get that natural 20. He will make every attack and every save, just look to his AC, perhaps well shielded Paladin or Cleric. Or just play him as an NPC who makes every skill check thrown at him.

However I strongly dislike fortune and misfortune hexes because rerolling takes up too much time, on that ground I wouldn't have allowed it. Perhaps you could time combat and tell that 6 attacks warrior that his rerolls make it take forever.
On the other hand fortune helps the party and is a very social hex which doesn't steal the spotlight from other players. I think people who don't try to kill everything themselves are rather likeable in general.

well bombs are good, as long as he manages his per days well and uses alchemists fire from time to time. I would go mindchemist and probably psychonaut too. (yes, smaller dice, but I would play him as kind of support with smoke bombs and throwing lots of alchmists fire, mainly damaging by superior intelligence)

If you have guns, then you can build an absolute damage powerhouse out of a vivisectionist (beast morpher). Sap master, double barreled pistols and a few modifications and you're good to go. Everything not immune to nonlethal damage will fall ... hard. However this build needs a few levels and some money to come together, however at the beginning you can just go for throwing knifes or something like that.
Also getting people flat footed is really important, so it's every so often a first round kill (you attack flat footed touch AC), which will ruin the GMs day, and once you meet someone you can't get flat footed you're humped. No means to deal extra damage, and nothing but a gun to attack.
I would discourage the last build, it's too restrictive and too "good", trust me the damage gets ridiculous.

edit: oh and you can probably skip the extra bombs. If you use fast bombs (and try to maximize the attacks per rounds) you will run out anyhow if you only throw bombs, no matter how many extra bombs.
I would rather use bombs for special occasion (and make them special with stinking bombs or similar) and throw your 6-7 alchemists fire per round with and int-bonus of 10 or something like that.

RAW against it, not really, but the item creation "guidelines" are not RAW, not everything you can create with it is reasonable.

My favourite example is putting multiple different amulet of mighty fists on one, instead of having a +5 equivalent one, you can have 5 times a +1 (equivalent) and it costs a lot less. (use 4 +1 for abilities because otherwise it won't stack).

Just don't allow it, because it would be homebrew anyway (only based on official guidelies). RAW items would be those written down in the books.

it depends on what you prefer to use in combat, if you help your group with evil eye, then go for the blouse. If you prefer to curse ennemies or use other hexes where the DC matters, then go for headband of vast int.

I would however go for the blouse as you've already got a headband of vast int and perhaps you can just skip the +4 and go directly to +6, thus saving some money. Also sometimes you just need that move action, and 23int is plenty at lvl 6.

From a purely optimizing point of view, +2 extra int is probably a tiny bit better.

Your second post is right, a full round action can include attacks from BAB and natural weapons. The vestigal arms help you have your hands free to claw the ennemy.

However even with vestigal arms you only have 2 secondary natural attacks.
From your first post I thought you meant you get 4 extra secondary natural attacks, which is (to my knowledge) false.
You should however be able to attack with your claws as normal weapons during your full attack routine.

For the accelerated drinker, I was referring to the work Paizo produced for the 3.5 rules set. Also I think it got errataed or FAQ (don't know about prehensile tail). If you ask your GM about the feat, I would recommend protective gear, because you're in fact asking to let a caster "cast" as a move action. Would you allow thiis to a bard or what is a magus good for if everyone can cast and attack?

my only addition would be that fireball is not an explosion there is no force, only temperature involved (at least this is the way I understand the spell).
While you may do some serious damage, it would not help you to get free any faster, altough you can try to eat your way out as the stomach wall should be cross.
If the creature is dead you should normally still need a piercing or slashing weapon to free yourself, or succeed on some kind of check to get out of the mouth again.

if you plan to take thoughness at some point, I would take it instead of slumber.

As others noted, slumber isn't that strong at the beginning.
And my personal reason is that slumber makes GMs hate you, it's an unlimited save or die ability. If you know the group and know that the GM can handle it and that it doesn't make the group feel useless (and that you never want to take thoughness), then I would recommend sleep as third hex at first level.

But Cackle and Evil eye would still be my first choice.

There is quite a good Witch guide by VikingIrishman or some name like that.

If you are 100% sure you want to take slumber, you might even want to consider to take improved initiative early on, altough that would mean that you get Evil Eye/Cackle far too late.

are you saying your animal companion doesn't drink water?
Just put it in a bowl for him.
Is this really something your GM has bothered you about, or do you want to ask as a preventative measure.
Also you could freeze it and serve it as crushed ice, inject it in meat, or put like gelatine in it (or whatever the magic dark-age alternative is).
This really should not cause concern.

1. Yes. I think there is like one important axis to consider, improvisation vs planning. Improvisation needs innate skill and is hard to learn, but if you're good at it GMing becomes very easy. Planning takes a lot of time that can be reduced by playing a premade adventure.
The best GMs are probably somewhere between those two, important points are planned, but can improvise when players act out.
I often need a short break when GMing for a couple of hours.
However GMing is mainly learning by doing, so in that aspect it's not rocket science, and it's no competition.

2.No, you don't get to play a unique hero with whom you can identify. However you can completly invent a world and every citizen therein, so in that aspect you get to play a lot.
Most people I know have a clear preference for playing, and GMing is fun but not as much fun as playing. The reason I have is that the GM doesn't feel like part of the group. Sometimes you play against the players, sometimes you play with them but have to restrain them from doing something. So it's like a parent and his children, you'll never really be part of your childrens playgroup, no matter how cool you are, but therefor you've got the money to buy whatever you want for yourself or your children.

@Namelessone
the problem is that (new in PF?) sneak attack from different base classes do not add up, which is very weird.
You add the class lvls, then look how much sneak attack that would make.

However as far as I know base attack bonus is still just added, a wizard, sorcerer, commoner, rogue etc. could still have a BAB of 0.

So the question, as I understood, is what happens if you add a prestige class with a different progression, if sneak attack dice are not added but considered as one big progression, even though the prestige class has a different progression chart than the rogue.

you understood one thing wrong I thing.
You do not determine the dice on sneak attacks by summing up the classes with that class feature, dividing it by two.
A rogue 1, vivisectionist 1, has 2d6 of sneak attack with 2 hit dice.

This problem with stacking isn´t a problem, except maybe at the second level. You won´t get the opportunity to get the advanced rogue talents for example, and 1d6 more isn´t going to break the game.
This would only become a problem if they add base classes or prestige classes (and not archetypes) that gain sneak attacks.

The difference is like a wizard gaining a spell level before the sorcerers. The third edition survived even without much balancing.

spelling errors in thread titles always remind me of the third edition barbarians for some reason.

Anyhow I believe the OP asked for complete immunities, not "very high saves". It´s easiest through race, so venturing in the bestiary would be my first step.
The second question you have to ask yourself is if you prefer several immunities to small conditions or rather 1-2 of the big ones.
The unbreakable fighter has a great capstone ability of being immune to mind-effects, quite broad. There is also a monk with the capstone of being immune to death effects and negative levels I believe.

A beast-bonded witch with a construct familiar is close to being a construct herself and profits of a ton of immunities.

So my entry is for elemental martial artist:
as monk: immunity to fatigue, immunity to exhaustion, immunity to stunning, immunity to death effects and energy drain.
as elemental:Immunity to bleed, paralysis, poison, sleep effects, and stunning.
and as secondary "immunities":
flanking, sneak attack, everything that causes eating, sleeping or breathing problems. (example: choke spell)

A Paladin and a Lich walk into a bar ...
sorry, I'm not sure I've heard that one before but here's my guess:

The Paladin fights him outside if possible.

Now I bet someone will ask, what if the lodge itself is the philactely of the lich, and it's impossible to kill it for good without breaking the rules.
Then the player punches the GM right in the face, there is no other outcome that is as satisfying and doesn't cause the paladin to break his code.

I love it, it feels more like the monsters out of myths, where some greenhorn has to slay a monster that has godlike powers except for that one weakness.
This last part would be a good addition in my opinion. Build-in weaknesses to certain attacks, for example vorpal weapons could cut off a minotaurs head on a 19-20. As it's low lvl, noone cares, but once you see that lvl 20 wizard minotaur throwing meteors in your face, you might want remember this.

my tips:
don't use too many monsters that use weapons or equipment, there are plenty that don't.
Do not let them discuss tactics in combat except short phrases, normally it's someone with an extraordinary talent for tactics that makes the difference.

Get bigger monsters. Elementals and Golems are my favorite.
Use the environment to your advantage, they don't have a wizard and can hardly control anything magical.
Every mundane fighter will fall, but perhaps they would enjoy a group of water elementals with their nets and disarms or even sunder attemps.

Also you've got an evil group, they can reduce pretty much any non-combat-challenge, to a combat-challenge.

sleeping is not the same as passing out.
They will probably have a hangover after medition, and they will pass out like any other person.
I mean they do pass out at -1 HP or if at 0 ability score (except con) so there is precedence for that.

I would say he's a bit like an older person, suspected to be a witch, lives outside of town because she's awkward and nobody likes her very much, but when the crops fail and the sheep die people know that she can help, but will shun her after she helped.
Of course you can manipulate while helping but if they don't feel that you personally have helped them, they are unlikely to want you close.

Also this feels like dirty munchkinism and you should be ashamed.
Good Luck nonetheless.

If you read Discworld novels, I would think of Granny Weatherhex when seeing those stats.

it's an exponential growth with a base around 1.2 (multiplied by a constant, perhaps around 5).
thus a round that would take 6 (5(1.2^1)) seconds with lvl 1, would take 5(1.2^20) 200 seconds at lvl 20.

ninja, sneaking around, materializing 5ft behind you when called, making your bed even though you locked the bedroom and have the only key.
Play him like a skill monkey with supernatural tricks (invisibility), having an assortment of wands of cure light wounds perhaps with the necessary use magic device.

My recommendation is witch, evil eye that AC. Your group horribly utterly lacks magic, a witch is the most arcane you can get without loosing on healing spells.
There is a wonderful Viking guide to witches somewhere around here to help.

If you want to join in and destroy stuff (the party seems to prefer kick-in-the-door-style), then an alchemist would do fine aswell.

However druids are a very good choice too, it's a bit less arcane than the witch, but got all kinds of fun spells.

I would even consider a summoner with that group, this way you add a bruiser, and have a character who can buff people all the time while still doing damage trough the eidolon.

at the very beginning of my RPG career, my GM told us once "and today you will fight the tarrasque", we were lvl 5 or something around that.
The only experienced player looked suspicious at the GM, but knew him good enough to know he had something up his sleeve.

And deep underground we found him, it as a mechanical, smaller copy of the tarrasque, and we killed it. I summoned 3 monkeys and he said "well how much damage do you expect them to do against metal", I smiled and said "I order them to screw and wrench at everything they can find", and while my comrades did HP-damage, my monkey did a good job as well, and we finished the fight in around 5 rounds.

being cool.
Well I imagine the witch as more distant, but she definetly doesn't get her hands dirty and is at least as much about magic as the wizard.
The cleric and the oracle don't wear shades as they want to see their god.

Which leaves us with the epitome of coolness, the alchemist.
Use magic device with wand of cure light wounds and that discovery to use your "spells" on other people and for the rest you have to decide if it's either physicical coolness (chuck a potion and smash someone in the face) or mental coolness (chuck a potion and outsmart everybody, and throw bombs while putting your sunglasses on).

As she's a woman I bet she goes for the latter, I would go mindchemyst, and perhaps psychonaut if you expect the game to last till later levels and she enjoys the power behind the throne kind of thing. Kirin strike is a nice feat to up the damage considerably with insane high intelligence.

On the other hand this is just my opinion and you can play every class in cool manner. The inquisitor can be like the Punisher, or the cleric like Captain America.
Don't expect however to be like monk or like a ninja, they can still heal with use magic device, but don't have such an innate ability.

healer has become very broad in PF
Witch has hexes for in-combat and can heal out of combat.
Alchemist has a good flavour for healing and can do fine.
Cleric, well it's obvious.
Oracle, perhaps even more focused than cleric, but might lack diversity.
Bard isn't all that bad either.

If she's into optimizing, she probably needs the last three to go with her stat boosts, but apart from that more input from her would be nice so we don't suggest the opposite of what she wants.

well there is the option of the insane vivisectionist with double barreled guns that has to catch him flat-footed and makes him unconscious using sap master and underhanded.

But aside from such crazy builds that only work if Lucifer stands right in front of you and wants a one on one match, I would go with other ideas.

Ask Asmodeus for help who can contract other gods to kill Lucifer.
Release the Tarrasque in hell.
Have a bloody big mob with leadership, equip them with vorpal swords and hope for lots of 20ies to roll.

Edit:
How about an adamantine golem with an intelligent item with special purpose "Kill Lucifer" and casting antimagic aura at will. This should take away every magic advantage Lucifer has, and he has no means to kill the golem. If the golem finds it difficult to grapple the prince of light and darkness, just get a few more adamantine golems in there.

the first question is actually two I believe
Yes you can walk on water, it counts as a surface.
I doubt that while submerged you can treat some water as surface and other like anything else. Plus I think you need a real swim speed to really "move" like that, being submerged is not difficult terrain but swimming. This answers question 2.

But feel free to houserule otherwise, I'm not that sure with the rules or if they even exist and giving "weak" classes a little bit extra is never wrong.